Controlling the roll angle of an aircraft during a turn such that the resultant force (comprising a vertical gravitational force and a centrifugal force) remains perpendicular to the floor of the cabin is known as making a coordinated turn. This is particularly important for passenger comfort as the weight of a person remains acting downwards relative to the person and relative to their seat, and any drink on a table appears level. Although the weight of the person increases slightly, they do not feel a lateral force.
A coordinated turn strategy for roll control has been applied to mono-hull boats using interceptors as disclosed in International Publication Number WO2011/099931 to overcome roll or heeling issues with propulsion pod marine vessels. Similarly it has been proposed for stability reasons to apply a coordinated turn strategy for roll control of a hybrid craft comprising a mono-hull connected under a small aircraft as disclosed in International Publication Number WO91/12172.
In the applicant's International Publication Numbers WO2011/143692 and WO2011/143694 are disclosed multi-hull vessels comprising suspension. The hulls are moveable relative to the deck or body portion and active (powered) control of the roll attitude of the body relative to the hulls is discussed. U.S. Pat. No. 3,517,632 also discloses a multi-hulled vessel in which the left hull and the right hull are moveable vertically relative to the body in dependence on steering angle to provide a lateral shift in the centre of mass of the body inwards towards the centre of the turn and also to tilt the hulls into the turn to enhance the steering effect without requiring a rudder. However controlling roll angle in dependence on steering angle without including a speed parameter does not vary roll angle in dependence on lateral acceleration, so does not provide a coordinated turn control.
In a conventional multi-hulled vessel such as a catamaran for example where the hulls are fixed relative to the deck or body portion, executing a coordinated turn requires the hull towards the inside of the turn to be moved downwards relative the water surface and the hull towards the outside of the turn to be moved upwards relative to the water surface. These changes in the displacement of the inner and outer hulls during a turn can provide significant hydrodynamic losses in efficiency and the inability to move the hulls relative to the body make executing a coordinated turn at planing speed impossible. Also the wider the spacing between the hulls, the smaller the range of possible controlled roll angles, so the lower the maximum lateral acceleration that can be compensated for through adjusting the vessel roll angle. For these reasons multi-hulled vessels of conventional construction, where the hulls are fixed, are generally unable to execute coordinated turns at speed.